A number of efficient methods have been developed for producing large libraries of variant genes and for expressing and screening those genes in a rapid and cost effective manner. A key element of any gene library-screening program is to maintain an association between gene and protein, so that when desirable variant proteins are identified, the genes encoding them can be recovered. One approach to maintaining the gene-protein correspondence is to distribute the clones into orderly arrays that can then be archived and replicated for expression and screening studies. While this is a straightforward and effective method for maintaining gene-protein correspondence, it is laborious and expensive to implement, especially with large libraries. Other approaches for manipulating and screening large gene-protein libraries involve display on the surface of virus particles or cells. These methods permit mass screening of many thousands to millions of variants. Most applications of display technologies have been based on prokaryotic systems and therefore do not provide for expression of proteins that may require expression in a eukaryotic host.
What is needed in the art is a eukaryotic expression system that supports expression of large libraries in a eukaryotic host while maintaining a correspondence between gene and protein. In conjunction, it may also be useful to employ an expression system that can produce larger amounts of protein than can be produced in a single cell.